first day of fermentation, a large inoculumof
a vigorous active-dry yeastmay
be required (even if no yeast addition
was originally planned). If non-Saccharomyces
yeasts reach 106/ml or more,
the populationmay need to be reduced
by centrifuging or filtering, before
inoculating with properly rehydrated
dry yeast.

Nutrient additions to uninoculated
fermentations should be delayed until
Saccharomyces is recognized under the
microscope, or until a clean-smelling
fermentation is under way. Fermentations
with more than around 10% non-
Saccharomyces yeasts should be considered
at high risk and carefully watched
for signs of sluggishness.

Lactic acid bacteria

Spontaneous growth of lactic acid
bacteria during fermentation can
sometimes be a positive occurrence, if
the bacterium is Oenococcus oeni, MLF
is desired, and no trouble in finishing
the yeast fermentation is expected. If
MLF is not desired, or if the yeast fermentation
could stick late in fermentation,
even Oenococcus can be a problem.
Never inoculate a struggling
fermentation with ML bacteria.

But if certain heterofermentative
Lactobacillus species (called “ferocious”
by Dr. Ralph Kunkee) grow
when there is fermentable sugar, the
result can be a disaster, traditionally
called “piqure lactique.” This is more
common in musts with higher pH
(>3.6). Besides converting malic to
lactic acid, they metabolize glucose
and fructose to acetic acid, raising VA
to 1 g/L or higher. Acetic acid, along
with toxins that at least some species
produce, is inhibitory to
Saccharomyces, and the fermentation
may stick. While Oenococcus is heterofermentative
and thus theoretically
could cause this type of spoilage, in
fact Lactobacillus is overwhelmingly
the bacterium responsible.

Lactobacillus spoilage may go undetected
until too late. Because Lactobacilli
do not make ethyl acetate, there
is no telltale odor,
and sugar can mask
the acetic “bite” at the
finish. Culturing
is not recommended because

wine
Lactobacilli grow very poorly in culture,
and often do not grow at all. PCR based
tests detect certain ranges of lactic
acid bacteria, but not necessarily all
wine Lactobacilli. For example, at present
the Scorpion test detects only
three wine species (L. plantarum, hilgardii,
and brevis), though others may be
responsible instead.

Microscopic examination easily
determines whether Lactobacilli of
any species are growing. If there are
enough cells to cause a problem,
there will be a large enough population
to see. Chemical tests can alert
the winemaker to check for
Lactobacillus: pH rise, drop in malic
or rise in lactic acid, and rise in
VA/acetic acid.

Stuck wines are extremely susceptible
to spoilage. The sugar offers a
substrate for a number of microbes,
and any efforts at encouraging completion
of fermentation, including
warming, aerating, and nutrient
addition, will also encourage spoilage
microbes.
To determine whether non- Saccharomyces
yeasts helped cause a stuck ferment,
take an unstirred sample and
then a stirred one.
In the settled lees, there may be
large numbers of odd-shaped yeasts,